Lithology for Museum Purposes. — Gratacap. 281 
A PLEA FOR THE POPULAR EXPOSITION OF 
LITHOLOGY FOR MUSEUM PURPOSES. 
By L. P. Gkatacap, New York. 
In public museums, enclosing the double purpose of in- 
structing- the people as well as meeting scientific requirements, 
the problems of presentation are frequently difficult. They 
can, however, quite usually, be solved by exacting some con- 
cessions from both the public and the student. The former 
consents to overlook technical precision and terminology, 
and find consolation in the beauties of the exhibit, and the lat- 
ter averts his eye from temporizing expedients of language 
and arrangement, content to enjoy the amplitude and variety 
of the collections. But in lithology it is very hard to interest 
the public at all by any superficial attraction in the specimens, 
and the scientific exposition in conjunction with them is too 
apt to leave in its mind only resentment and impatience. Yet 
lithology demands a place in our museums and as it has been 
recognized abroad must be somehow thrust upon the average 
visitor — a conipound of ingenuous curiosity and self-respecting 
intelligence — here as well. 
In considering some possible system for the achievement of 
this purpose the following scheme is suggested, which can, in 
its specific details, be much varied. The subject can be bro- 
ken up or divided under seven heads, i. Idea of Rock; 2. 
Terms; 3. Physical Condition; 4. Lithologic Processes; 5. 
Classification ; 6. Distribution ; 7. Life History ; 8 . Geolog- 
ic Occurrence. 
I. Idea of Rock. 
The average man has a poor or incomplete conception of 
the scientific implications of a rock, and while he apprehends 
clearly enough the geographical extent of rocks, perhaps their 
physical properties, he fails to realize their mineral nature, and 
utterly their classification and relations. The Idea of a Rock 
can be expressed by, firsts the mechanical analysis of a rock, 
the separation of granite into mica, quartz, and feldspar, the 
unbroken fragment of granite, and the separated piles of grains 
of its mineral elements: the separation of doleryte into augite 
and labradorite, with accessories of hornblende, (|uartz, 
magnetite, olivine, etc., and the peeling apart of a 
sandstone into its constituent grains. In all such physical 
